The present invention relates to specially processed fasteners, and, more particularly, to apparatus and methods for the manufacture of fasteners having a resin material applied to achieve a self-locking or sealing function or for other purposes well known in the art.
There are a variety of ways to apply a resin coating to a fastener. Many devices and methods have been developed and directed toward this purpose. One common technique involves the deposition of powdered resin by passing the fastener through a gravity induced cascade of the resin as shown in prior art patents such as U.S. Pat. No. 3,830,902 (Barnes) and U.S. Pat. No. 3,286,964 (Burgess). Another technique employs entrainment of the powdered resin in an air stream and spraying the resulting air entrained powder through a nozzle toward a passing fastener as shown in U.S. Pat. No. 3,498,352 (Duffy). To prevent waste of the powdered resin that bypasses the fastener during the referenced processes, others have proposed the use of vacuum devices that collect and recirculate the excess powder such as U.S. Pat. No. 5,836,721 (Wallace).
Among the known disadvantages of the gravity feed process is the lack of precision in the deposition of the powdered resin. An excessive powder flow rate is commonly induced to insure that at least the minimum required quantity of powder is applied to the fastener, resulting in an undesirable level of waste or excessive recirculation of the resin which can diminish the quality of the resin materials. Entrained air spraying processes reduce waste and improve precision, but with a concomitant increase in cost. Use of the spraying process requires a higher energy demand to generate the pressurized air stream and to preheat the fasteners in advance of the powder application. Moreover, the compressed air typically used in such processes is preferably cleaned to remove moisture and oil to minimize powder contamination. The preheated fastener required by the spraying process creates a condition where the powder coating is instantly bonded to the fastener, thereby preventing removal of the resin inadvertentaly deposited onto areas of the fastener where the coating is not required or desired.
It would be advantageous, therefore, to have a powder application system for applying coatings on fasteners having the cost benefit of the gravity feed process while retaining a measure of the precision of the air spray process. It would further be advantageous to retain the ability to clean excess powder from the fastener prior to heat bonding.
The present invention is directed to an apparatus and a method for applying a powdered resin coating to a fastener that incorporates a combination of adjustably positionable gravity deposition and vacuum recirculation components so as to overcome the limitations of the prior art.
The present invention is, therefore, an apparatus and a method for applying a resin coating to a fastener. A reservoir for the powdered resin materials is provided with a discharge means that has an adjustably positionable free end. The discharge means or conduit forms a gravity induced cascade for feeding the resin material onto the fastener. Variation in the dimensions of the discharge conduit allows for a variety of configurations for the cascading powder stream leaving the free end. Fasteners are passed through the powder stream by conveyor means. Adjacent to the powder stream and the conveyor carried fasteners, an adjustably positionable vacuum nozzle is provided to collect excess resin. The ability to adjust the spatial and positional relationship of the discharge conduit and the vacuum nozzle allows more precise control over the location and amount of powdered resin material that is deposited on the fastener. Following the powder deposition and collection steps, the fasteners are passed through a heating means to permanently fuse the resin material to the fastener.
In a preferred embodiment, the conveyor means is a rotating carousel with a means for rotating individual fasteners as they pass through the powder stream. One potential means for rotating the fasteners involves the application of vertical posts to the rotating carousel. The posts can be adjustably spaced to accommodate a variety of fastener sizes. A fastener is placed in a fixed position at the top of each post, and the rotation is accomplished by means that make the posts themselves rotate.
Another preferred feature of the invention is the inclusion of a means for vibrating the reservoir to assist in control of the feed rate of the resin material into the discharge conduit. The discharge conduit may also include an adjustable input baffle at the head of the discharge conduit to provide for further control of the feed rate. Additionally, a means for adjusting the negative pressure on the vacuum nozzle provides still further control over the removal of excess deposited resin material on the fasteners.